Lathes designed to mount on a work bench to machine automotive brake discs, e.g. rotors, have been in existence for many years. Many of these lathes machine both brake discs and brake drums. The brake disc is removed from the vehicle and mounted to the spindle of the bench mounted brake lathe. More recently, a new type of lathe was developed that machines the brake disc without removing the brake disc from the vehicle, in other words a disc brake lathe that machines the disc on the vehicle.
The first on-the-vehicle disc brake lathes used the vehicle's engine power to rotate the brake disc during machining. Later, a separate power drive unit was added. More recently, the drive unit and the lathe have been combined in one integrated version. See U.S. Pat. No. 4,226,146. While on-the-vehicle brake lathes are intended to perform a similar function to bench mounted lathes as to machining a brake disc, there have been problems with prior attempts to make a light weight, fully functional on-the-vehicle disc brake lathe with similar features and functional capability to a bench mounted lathe.
Disc brake lathes are subject to vibration. Vibration can occur as the metal is being cut from the often uneven surface of a used brake disc or due to inconsistencies in the hardness of the brake disc material itself. This vibration can cause the rotor to resonate or ring like a bell and cause a poor surface finish on the rotor. Bench mounted lathes and other metal machining tools address this problem by making the lathe or tool very heavy such that the mass thereof sometimes is nearly one hundred times the mass of the brake disc. However, such a solution is not practical in an on-the-vehicle disc brake lathe where, in order to make the lathe easily portable, it is preferred that the weight or mass of the lathe head be limited to about five times the weight or mass of the brake disc. In machining a brake disc with an on-the-vehicle disc brake lathe, as long as the wheel bearing on the vehicle is sufficiently strong and rigid to make a solid connection between the brake disc and the mass of the car, vibration is not a problem. However, in some cases the bearing may have some small amount of play and the brake disc is therefore free to impart vibration to the lathe head. There is a need for an improved on-the-vehicle brake disc lathe which reduces or eliminates vibration of the lathe head thereby permitting an improved machined surface finish on the brake disc and increased machining speed.
During set up and machining of a brake disc with the conventional on-the-vehicle disc brake lathe, the brake disc on the vehicle and the coupling mechanism connecting the power drive to the brake disc are rotating at high speed. Under these circumstances there is a hazard in that the operator's clothing or power cords for the lathe could possibly become entangled in the rotating parts. There is a need for an improved on-the-vehicle disc brake lathe permitting safer use of the brake lathe.